Manage your subscription

Quantum socks are more tangled than that

Published 11 April 2017

From
Paul Dormer, Guildford, Surrey, UK

Brian Horton hasn't quite got there with his sock analogy for quantum entanglement (Letters, 1 April). The thing with quantum entangled particles is that there are two ways to perform the measurement of the entangled property – up/down or left/right to put it simply – and you have to decide in advance which measurement to make.

So if you have four quantum entangled socks, two red and two green, and you get dressed in the dark, it all depends on which foot you look at first.

If you decide to look at your left foot first and you have on a red sock, then you know your partner, if they look at their left foot, has on a green sock. Similarly, if you both look at your right foot. But if you look at your left foot and your partner looks at their right foot, then you can make no prediction. Fifty per cent of the time you will have on socks of the same colour.

Furthermore, once you have looked at one foot, if you look at your other foot, the sock there will have mysteriously turned grey, as will your partner's.